The present invention relates to a semiconductor device including semiconductor chips packaged therein, and more particularly to a semiconductor device including semiconductor chips packaged therein with high density where the semiconductor chips are buried in a printed wiring board, and a method for fabricating such a semiconductor device.
In recent years, electronic equipment, in particular portable electronic equipment, has been downsized at rapid paces. To keep pace with this, downsizing of semiconductor devices is also in progress. For example, small-size semiconductor packages such as chip scale packages (CSP) have been commercialized. Also commercialized have been semiconductor packages in which semiconductor chips are stacked on top of each other to reduce the packaging area of the semiconductor chips. Moreover, for attainment of further thinned electronic equipment, there have been developed semiconductor devices including semiconductor chips packaged therein with high density where the semiconductor chips are buried in a multilayer wiring board.
Hereinafter, as a conventional example, a semiconductor device and a fabrication method thereof disclosed in Japanese Laid-Open Patent Publication No. 4-373157 will be described with reference to FIGS. 30A through 30C.
FIGS. 30A through 30C are cross-sectional views illustrating process steps of a conventional method for fabricating a semiconductor device.
As shown in FIG. 30A, an insulating board 13 having an opening 13a is bonded to the top surface of a first circuit board 10. The first circuit board 10 has first and second wirings 11 and 12 formed on the top and bottom surfaces thereof. A semiconductor chip 14 is mounted on the exposed top surface of the first circuit board 10 inside the opening 13a so that the circuit formation surface of the semiconductor chip 14 faces the top surface of the first circuit board 10, that is, by face-down bonding. To state more specifically, bumps 15, which are formed on electrodes (not shown) provided on the circuit formation surface of the semiconductor chip 14, are bonded to the first wiring 11 with conductive paste 16. A first resin layer 17 is then formed between the semiconductor chip 14 and the first circuit board 10.
As shown in FIG. 30B, a second resin layer 18 is formed on the sides and the top surface of the semiconductor chip 14 so that the opening 13a is filled completely. Thereafter, as shown in FIG. 30C, a second circuit board 20 is bonded to the top surfaces of the insulating board 13 and the second resin layer 18. The second circuit board 20 has third and fourth wirings 21 and 22 formed on the top and bottom surfaces thereof.
By the fabrication through the process steps shown in FIGS. 30A through 30C, completed is a semiconductor device where the semiconductor chip 14 is buried inside the multilayer circuit board composed of the first circuit board 10, the insulating board 13, the second circuit board 20, and the like.
The conventional semiconductor device described above has the following problems. The opening 13a must be formed through the insulating board 13 constituting the multilayer circuit board, to mount the semiconductor chip therein. This increases the number of fabrication steps and thus increases the cost. In addition, the first wiring 11 may be contaminated with an adhesive material and the like flowing out during the bonding of the insulating board 13 to the first circuit board 10. This makes it difficult to keep clean the connecting portions of the first wiring 11 with the semiconductor chip 14, and thus to ensure the electrical connection between the first wiring 11 and the semiconductor chip 14. Another problem is that separation is likely to occur at the interface between the insulating board 13 having the opening 13a and the second resin layer 18 filled in the opening 13a. This makes it difficult to attain a good-quality semiconductor device.
In order to reduce the thickness of the entire semiconductor device including semiconductor chips packaged therein, the semiconductor chips must be thin. A thin semiconductor chip is more susceptible to external damage and more easily warped losing flatness, compared with a thick semiconductor chip. Therefore, when a thin semiconductor chip is used for the conventional semiconductor device, difficulty arises during the formation of bumps and the mounting of the semiconductor chip in the board. In other words, in order to prevent a semiconductor chip from external damage and warping in the conventional semiconductor device, a thick semiconductor chip must be mounted. This increases the thickness of the multilayer circuit board constituting the conventional semiconductor device. In addition, since a thick semiconductor chip is buried with a resin in the multilayer circuit board, heat generated due to the operation of the semiconductor chip is less easily dissipated outside.